1. Field of the Invention
The present invention relates to an automatic transmission that is mounted on a vehicle such as a car.
2. Description of Related Art
In an automatic transmission disclosed in Japanese Patent Application Publication No. 2007-132421 (JP 2007-132421 A), an output gear is supported by a cylindrical portion of a transmission case through a radial bearing.
Outer circumferential teeth of the output gear are teeth of a helical gear. The radial bearing is a double row angular contact ball bearing, and is located with respect to the cylindrical portion of the transmission case in a shaft direction. The radial bearing is located using a retaining ring. The retaining ring is locked across an outer circumferential groove that is provided in an outer circumferential surface of an outer ring of the radial bearing, and an inner circumferential groove that is provided in an inner circumferential surface of the cylindrical portion of the transmission case.
A piston that applies a pressure to friction engaging elements (brake) that control, gear shifting is slidably fitted to an exterior of a radial bearing support region in the cylindrical portion of the transmission case. Further, a return spring that urges the piston in a direction to separate the piston from the friction engaging elements when no pressure is applied is disposed in the support region of the cylindrical portion of this transmission case. This return spring is retained by the retaining ring that is locked in the outer circumferential groove of the cylindrical portion of the transmission case.